What Is a Butt Weld Equal Tee?
A butt weld equal tee is a T-shaped pipe fitting in which the branch outlet has the same outside diameter as the main run. It is used when a branch line of the same size must be taken off a main line, allowing fluid to be diverted or merged without changing pipe size.
The fitting is connected by butt welding: the pipe ends are beveled, aligned and joined with full-penetration welds. Because the weld is made on the outside of the beveled joint, the internal bore remains smooth and the fitting carries the full pressure rating of the connected pipe. Equal tees are the most common branch fitting in industrial piping systems.
Standard and Dimensions
Butt weld equal tees are manufactured to ASME B16.9, which defines the dimensions, tolerances and marking of factory-made wrought butt-welding fittings. The key dimension is center-to-end: the distance from the centerline of the run to the end of the branch, and from the branch centerline to the end of the run. For an equal tee these two values are identical.
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| Nominal Pipe Size | Outside Diameter at Bevel (mm) | Center-to-End Run C (mm) | Center-to-End Outlet M (mm) |
|---|---|---|---|
| 1/2 | 21.3 | 25 | 25 |
| 3/4 | 26.7 | 29 | 29 |
| 1 | 33.4 | 38 | 38 |
| 1-1/4 | 42.2 | 48 | 48 |
| 1-1/2 | 48.3 | 57 | 57 |
| 2 | 60.3 | 64 | 64 |
| 2-1/2 | 73.0 | 76 | 76 |
| 3 | 88.9 | 86 | 86 |
| 4 | 114.3 | 105 | 105 |
| 6 | 168.3 | 143 | 143 |
| 8 | 219.1 | 178 | 178 |
| 10 | 273.0 | 216 | 216 |
| 12 | 323.8 | 254 | 254 |
| 16 | 406.4 | 305 | 305 |
| 20 | 508.0 | 381 | 381 |
| 24 | 610.0 | 432 | 432 |
The wall thickness of the fitting matches the schedule of the connecting pipe, so that the weld joint is made between equal thicknesses and the pressure rating is maintained across the fitting.
Materials
Equal tees are available in carbon steel, alloy steel and stainless steel. The most common carbon steel material is ASTM A234 Grade WPB, which is the fitting counterpart of A106 Grade B pipe. For low-temperature service, A234 WPL6 is used; for high-temperature alloy service, A234 WP11 and WP22 are common. Stainless steel tees are normally supplied to ASTM A403. The material grade is stamped on the fitting and must match the pipe specification for the service.
Manufacturing
Butt weld tees are manufactured by hot forming from seamless or welded pipe or plate. The branch is formed by extrusion or forging, and the fitting is then heat treated to restore the required mechanical properties. Larger tees may be fabricated from formed segments and welded. After forming, the ends are machined to the bevel profile and the fitting is dimensionally checked and pressure tested where required.
Applications
Equal tees are used wherever a full-size branch is taken from a main line: process piping in refineries and chemical plants, utility piping, water distribution, fire protection, and oil and gas gathering systems. The smooth bore and full-size branch make the equal tee suitable for piggable lines and for services where pressure loss across the branch must be minimized.
Installation and Welding Guidance
Clean and inspect the bevels before welding, and verify the fitting grade and schedule against the line specification. Align the branch perpendicular to the run using a spirit level or alignment fixture, and tack weld before completing the joint. Use a qualified welding procedure for the material grade and wall thickness. After welding, carry out the required inspection, typically visual and either radiographic or ultrasonic examination for critical service.
Common Misconceptions
A common error is confusing an equal tee with a reducing tee; in a reducing tee the branch is smaller than the run, and the center-to-end outlet dimension differs. Another error is assuming the tee wall is always the same as the pipe; the fitting schedule should be verified because fittings are sometimes supplied in a heavier schedule than the pipe. A third mistake is using an equal tee where the branch flow is much smaller than the main flow, which causes unnecessary pressure loss; a reducing tee or a weld outlet is often better.
FAQ
What is the difference between an equal tee and a reducing tee?
In an equal tee the branch has the same diameter as the run. In a reducing tee the branch is smaller, and the center-to-end dimension of the outlet follows the smaller size.
Which standard covers butt weld equal tees?
ASME B16.9 covers factory-made wrought butt-welding fittings including tees, defining dimensions, tolerances and marking. Material grades follow ASTM A234 for carbon steel fittings.
What is A234 WPB?
A234 WPB is the most common carbon steel fitting material, equivalent in strength to A106 Grade B pipe. W means wrought, P means pipe fitting and B is the grade.
Can an equal tee be used in piggable pipelines?
Yes. A full-bore equal tee with smooth internal surfaces and no protrusions can be traversed by pigs, provided the branch is not obstructing the run bore.
How is the branch welded to the pipe?
The pipe ends and the tee outlets are beveled, aligned and joined by full-penetration butt welds using a qualified procedure for the material and wall thickness.
What sizes are available?
ASME B16.9 covers tee sizes from 1/2 inch up to 48 inch and beyond, with the center-to-end dimensions for sizes up to 24 inch tabulated above.